The present invention relates to a system and method for distributing a low vapor pressure gas to one or more points of use through a distribution conduit communicating at opposite ends with the head space of a vessel containing the low vapor pressure gas as a vapor phase of a substance. More particularly, the present invention relates to such a system and method in which the low pressure gas is continually circulated through the distribution conduit and the head space of the vessel.
In a variety of chemical processes, particularly those utilized in connection with semiconductor processing, high purity, low vapor pressure gases are distributed to points of use which can be the reaction chamber of a semiconductor production tool. These gases include: trichlorosilane (SiHCl.sub.3) boron trichloride (BCl.sub.3), hydrogen fluoride (HF), tungsten hexafluoride (WF.sub.6) and silicon tetrachloride (SiCl.sub.4). The invention also has applications for other gases used in the semiconductor industry for oxide-metal chemical vapor deposition, oxidation, doping, diffusion, ion implant, and the like. Where the vapor pressure of some aforementioned gases is below atmospheric pressure, they cannot be directly distributed to the process tooling. Instead, the particular gas to be distributed is introduced as a liquid into a vessel and a carrier gas is sparged into the liquid to produce a saturated vapor. The saturated vapor is then piped to various tools within the semiconductor production facility.
This aforementioned type of distribution is not without problems. Semiconductor factories are increasing in size, the distribution system must grow to meet the increased flow requirements. As demand varies in the facility, the saturated gas flow will also vary. At low flow rates, pipe line contents will tend to stratify thus causing separation of the carrier gas from the saturated vapor. In addition to the forgoing, since the liquid in the vessel can be warmer than the saturated gas in the distribution system, there will be some degree of liquid condensation within the pipeline. Such liquid condensation can also occur due to pressure variations within the pipeline. The appearance of liquid can in turn cause an automatic shutdown of certain semiconductor processing tools and thus, an expensive lapse in production capability.
As will be discussed, the present invention provides method apparatus in which a saturated gas is formed and distributed in a manner that is less susceptible to liquid condensation than prior art methods of distribution.